Chloride is the name for the Cl- ion. Since most things are soluble in water, almost any chloride (for example, table salt, NaCl) will contribute Cl- to the solution. AFAIK elemental chlorine is not actually used as a disinfectant; water treatment plants probably use hydrochloric acid (HCl) which in water tends to dissociate into H+ and Cl-.

And yes, campden will strip out chlorine and chloramines. It will actually increase chloride (and sulfate) concentration.

HCl would only be used if there were too much alkalinity (pH way too high), at the plant. It's important to keep some alkalinity in water because the piping will dissolve in acidic conditions (sometimes a problem for people w/copper pipes and well water). Most likely choramine or hypochlorite is used. These produce small amounts of hypochlorus acid that is the species that is the actual disinfectant.

Sulfite ion is readily oxidized to sulfate. On prolonged exposure to air, this oxidation occurs with atmospheric oxygen:

I wonder what the contributions of the two ions are from the campden.Maybe one day I'll send in two identical water samples for tseting except one will have been treated with campden.Also, Isn't campden a sulFITE? Why would that raise the sulFATE level?

It's actually sodium (or potassium) metabisulphite, Na2S2O5. It will react with water to form sodium bisulfite, which then neutralizes the chloramines:

NaHSO3 + NH2Cl + H2O -> Na+ + H+ + Cl- + NH4+ + SO42-

It looks like the average campden tab is about 0.5 g, so assuming my stoichiometry is right a typical homebrewer dose (one tab in 9 gallons) would add about 1.8 ppm sodium, 2.7 ppm chloride, and 7.3 ppm sulfate. If you ever do get your water tested before and after, let me know; I'd like to see how closely it matches up with the theory.

The chloramines are NH2Cl and NHCl2 and the sulfites (SO32-) come from the campden tablets. As you can see the reaction does leave sulfates and chlorides in the water. It also produces ammonium ions, which gas off as ammonia or change to nitrates. I don’t want to speculate here.